大黄素对大鼠近端结肠平滑肌细胞电压依赖性钾通道的影响

Emodin blocks voltage dependent potassium channels in rat proximal colon smooth muscle cells

目的研究大黄素对大鼠近端结肠电压依赖性钾离子通道的影响,以探讨其增强结肠运动的机制。方法采用全细胞膜片钳技术测定电压依赖性钾离子通道快速激活型钾电流及延迟整流型钾电流。结果大黄素(1～30μmol·L-1)浓度依赖性地阻断延迟整流性钾通道,加快电流失活,其阻断作用不需要钾通道的开放。30μmol·L-1大黄素可抑制快速激活型钾电流。5μmol·L-1大黄素对钾通道的激活动力学及失活动力学没有影响,但30μmol·L-1大黄素使其激活动力学曲线明显右移,斜率常数由(13.0±0.6)上升至(19.6±2.5)mV,同时也使失活动力学曲线明显右移。结论大黄素可阻断延迟整流型钾通道及快速激活型钾通道,其阻断作用不是开放阻断。

Aim To investigate the effect of emodin on the voltage dependent potassium （Kv ） currents in rat proximal colon smooth muscle cells. Methods Whole cell patch clamp technique was used to record potassium currents including fast transient outward current （IKA） and delayed rectifier current （/Kdr）. Contamination of calcium-dependent potassium currents was minimized with CdCI2 in external solution and EGTA in pipette solution. Results Emodin （1-30μmol·L^-1） reversibly and dosedependently reduced the amplitude of IKdr with an Kd value of （ 1.9 ± 0. 1 ）μmol·L^-1. IKA was also inhibited with 30μmol·L^-1 emodin to a lesser extent. Although acceleration of the decay rate of the Kv currents was observed, the block by emodin was not through open block mechanism because a steady state level of inhibition of IKdr was achieved during the first pulse from holding potential - 70 mV to ＋ 50 mV after the cells were holding at - 70 mV for a three minutes interval in the presence of emodin. Emodin （5 μmol·L^-1 ） had no effect on the steady-state activation and inactivation kinetics of Kv currents, but 30μmol·L^-1of emodinproduced a positive shift of the voltage dependence of activation, and an increase in the steepness of activation gating as well as shifted the voltage dependence of inactivation to positive direction. Conclusion Emodin, not through open block mechanism, markedly reduced the amplitude of IKA and IKdr and modulated the gating properties of Kv channels in a reversible and dose-dependent manner.